Communications via optical fiber is mature technology. Electronic signals are converted to light signals and the light signals are coupled to an optical fiber which carries the optical signals over the optical link. At the other end of the optical fiber link a photo detector converts the light signal to an electronic signal completing the connection. The means of converting the electronic signal to an optical signal for example employs laser diodes for long distances at very high speed and light emitting diodes for medium distances at high speed.
The means to couple signals from light emitting diodes and laser diodes to optical fiber is well established in the art. U.S. Pat. No. 5,448,676 describes means to align a light emitting diode to the centre of the fiber, U.S. Pat. No. 5,631,992 stresses the use of a rod lens to couple the light source to the optical fiber, and U.S. patent publication number US 2007/0031089 describes means to couple light in a highly efficient method. U.S. Pat. No. 4,466,696 further describes similar coupling of laser diodes or light emitting diodes to optical fiber for the same means to form a communications link between two points. All these methods require mechanically matching the emission angle of the light emitting source to the acceptance angle of the optical fiber by employing intermediary optical equipment.
An ongoing challenge in coupling light emitting diodes to an optical fiber is the mismatch in the physical dimensions of the light emitting diode and the optical fiber. Nominally a multimode optical fiber has a diameter of 60 to 100 microns. A light emitting diode is at least three times larger, nominally 300 microns. Most of the light is lost unless refractive optics are used to converge the light into the optical fiber. In the case where laser diodes are used, which have a smaller emission angle and a small aperture, the cost of the laser diode and the emission angle pose the same problem as with a light emitting diode.
Light emitting diodes, though far lower in cost and suited for medium distances, are still not considered for short distances. This is due to cost constraints. Communications over long and medium distances can carry vast amounts of data at very high speed and the cost is easily amortized over the traffic. At short distances, the amount of data is much less and has to be amortized usually over a single user. One example of this short distance communications problem is referred to as the “last mile problem”. It is feasible to bring optical fiber to a common point in a community and this is common practice. From this common point, connecting to each user via an optical cable link is prohibitive and limits the bandwidth which can be provided to each user. This “last mile” link is presently connected via copper conductors which have limited bandwidth.
There is a need for means of coupling light emitting diodes to an optical fiber, namely without the use of any secondary devices such as refractive optics and mechanical holding devices.